Preserved plants have story to tell about climate change

Herbaria are collections of dead plants, mostly pressed and dried. Around the world there are hundreds of millions of these preserved plants stored in botanic gardens, natural history museums and universities.

The 1.2 million specimens in the National Herbarium of New South Wales, held in Sydney's Royal Botanic Gardens date back to Joseph Banks and Daniel Solander's visit to Botany Bay in 1770. The collections represent 240 years of collecting in Australia and provide the scientific evidence behind the discovery and description of the 20,000 or so species of Australian plants.

It often comes as a surprise to learn that herbaria hold more than one specimen of each species. We do this to cover the geographic range of the species as well as its variation in shape and form. A herbarium specimen is a reliable and verifiable piece of scientific data, one that can be checked and tested at any time. You can't do this with a dot on a map.

Recently we have taken advantage of the changes over time as well. For example there is some powerful information held in herbaria about changes in flowering time over the last few centuries, with the potential to track the impacts of climate change on our natural world.

ScienceDaily reported a few weeks ago on one such study. Headed 'Ecologists Find New Clues on Climate Change in 150-Year-Old Pressed Plants', the report was based on a paper just published in British Ecological Society's Journal of Ecology.

It's argued, quite correctly, that the shortage of long-term data on seasonal changes is hampering our understanding of how plants and animals respond to climate change.

This latest research is a collaborative effort by scientists from the Universities of East Anglia, Kent and Sussex, as well as Kew Gardens which has a 7 million strong collection in its herbarium.

It was a small study but it points to the kind of valuable information held in this world-wide network of herbaria. 77 herbarium specimens of the Ophrys sphegodes, the Early Spider Orchid were correlated against climate records over the time they were collected, between 1848 and 1958.

This data was compared with field observations made in a local nature reserve at Castle Hill in East Sussex between 1975 and 2006. Lo and behold, as we say in science, the correlation between flowering time and temperate was the same in the herbarium as in the reserve: "the orchid flowered 6 days earlier for every 1oC rise in mean spring temperature".

ScienceDaily says these results are the first to show that preserved plant collections can be used to study the relationships between seasonal change (phenology) and climate change, and can be a substitute for field observations.

Lead author and PhD student, Karen Robbirt, is quoted as saying: "We found that the flowering response to spring temperature has remained constant, despite the accelerated increase in temperatures since the 1970s. This gives us some confidence in our ability to predict the effects of further warming on flowering times."

With some 2.5 billion specimens of plants and animals preserved in the world's herbarium and museum collections, there is plenty of potential to find out more about changes over the last few centuries as we predict and adapt to changes over the next few.

I'd still argue for good long-term field studies - including some experimental manipulation - but this is a timely reminder that herbaria are a vast and largely untapped treasure trove of information.

Image: the 'red boxes' that hold the 1.2 million preserved plants held in the National Herbarium of New South Wales, and an example of a herbarium specimen